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Asynchronous SRDF (SRDF/A) is a method of replicating production data changes from one PowerMax to another using delta set technology. Delta sets are the collection of changed blocks that are grouped by a time interval that can be configured at the source site. The default time interval is 30 seconds. The delta sets are then transmitted from the source site to the target site in the order that they were created. SRDF/A always preserves the dependent-write consistency of the database at the remote site. For more details about SRDF/A, see the Dell support site.
The distance between the source and target PowerMax is unlimited and there is no host impact. Writes are acknowledged immediately when they approach the cache of the source PowerMax. The following steps outline the basic process:
The multi-cycle mode on the PowerMax employs a queuing mechanism that allows for smaller delta sets to be transferred, reducing RPO. Multimode representation is in Figure 178.
Before the asynchronous mode of SRDF can be established, an initial copy of the production data must occur. In other words, a baseline of all the volumes that are going to participate in the asynchronous replication must be performed first. This task is usually accomplished using the SRDF adaptive copy mode which is more efficient for this initial bulk-load. Once the task is complete, the mode is changed to asynchronous.